Exhaust gas generated from various types of stationary combustion devices such as a boiler, a private power generator, and a combustion furnace, and metal etching contains a nitrogen oxide (NOx). The nitrogen oxide (NOx) is a substance causing photochemical smog. For this reason, it is necessary that the nitrogen oxide be purified by a denitration device.
Such a denitration device has a denitration catalyst layer in which many catalyst blocks are spread. FIG. 11 is a schematic view of a conventional catalyst block as viewed in a gas flow direction. With reference to FIG. 11, a block for a catalyst 100 is configured so that a rectangular honeycomb core 101 in which a corrugated plate and a flat plate are alternately layered is enclosed in an outer frame 102.
The outer frame 102 is constituted by a C-shaped frame 102a and a top frame 102b. As shown in FIG. 12 that shows a Z1-Z2 cross section of the catalyst block, the C-shaped frame 102a has a clearance CL sufficient to insert the honeycomb body 101. The block for a catalyst 100 is immersed in a catalyst bath, and then baked. Thus, a catalyst is carried on the block for a catalyst 100.
As another conventional technique, Patent Literature 1 discloses a denitration catalyst layer in which catalyst blocks each having a frame body and a catalyst contained in the frame body are entirely spread and layered. In the denitration catalyst layer, a plate-shaped catalyst is attached to a circumference of the frame bodies of the catalyst blocks. This is a technique of removing a nitrogen oxide from exhaust gas flowing out from a gap formed between the catalyst blocks using the plate-shaped catalyst, to decrease NOx and the like at an outlet of the catalyst layer.